In recent years, there has been an increasing demand to improve the display quality of active matrix displays each including many switching elements, such as TFTs (thin film transistors). However, higher definition of display involves shrinking patterns of lines, etc., on a substrate. This makes it difficult to completely prevent display defects (including unlit dots) due to a break in the lines, etc., or shorting between adjacent ones of the lines.
For example, open defects in a TFT may occur where the TFT is always OFF. Alternatively, charge leakage (shorting) from an auxiliary capacitor may occur. Furthermore, degraded characteristics of a TFT may arise from failures in carrier doping for the TFT.
These defects may lead to display defects where bright spots are always displayed. The display defects where bright spots are always displayed are conspicuous to users. Therefore, they have been known to be repaired in the following manner: defective pixels are displayed in black by creating a short circuit between a gate line and a drain of a TFT,
Specifically, in a normally white liquid crystal display, a short circuit is created between a drain of a TFT of a defective pixel and a corresponding gate line, and thus a relatively high voltage is generally continuously applied to a liquid crystal layer by a pixel electrode shorted to the gate line through the drain and a counter electrode (common electrode). As a result, the defective pixel is always displayed in black.
In PATENT DOCUMENT 1, an area of a TFT occupied by both its gate electrode and its drain electrode is irradiated with laser beams. Thus, a gate insulating film is destroyed so that the gate electrode and the drain electrode melt to allow electrical connection therebetween. A scan pulse is applied to liquid crystal material through a display electrode connected to the drain electrode. As a result, a corresponding pixel appears dark in a normally open mode, and therefore becomes less prominent.
PATENT DOCUMENT 2 describes that, in an active matrix display, a short circuit is created at a plurality of positions between a TFT corresponding to a defective pixel appearing as a bright spot and a line for repair by laser irradiation, thereby changing the bright spot to a black spot.
Furthermore, PATENT DOCUMENT 3 describes that, when a defective bright spot results from charge leakage from an auxiliary capacitor, a corresponding pixel electrode is cut into pieces so that a region of the auxiliary capacitor from which charges leak is located between outer ones of the pieces, and a short circuit is thus created between a drain of a corresponding TFT and a corresponding gate line, thereby displaying a corresponding pixel in black.
PATENT DOCUMENT 1: Japanese Patent Publication No. 5-210111
PATENT DOCUMENT 2: Japanese Patent Publication No. 4-324819
PATENT DOCUMENT 3: Japanese Patent Publication No. 2002-341379